基于变速积分PID的电热锅炉温度控制系统设计与仿真

本文设计了基于AT89s51的水温控制系统

工机电工程技术年第38卷第12期

基于变速积分PID的电热锅炉温度控制系统设计与仿真

徐志强，秦付军

（西华大学机械工程与自动化学院，

四川成都

610039）

单片机为核心，采用变速积分PID控制的电热锅炉温度控制系统，。单片机；变速积分PID控制文献标识码：B

文章编号：1009－9492(2009)12－0024－02

1引言

温度是工业控制中主要的被控参数之一，特别是在冶金、化工、建材、机械等工业中，具有举足轻重的作用。对于不同场所、不同工艺，以及不同的温度范围、精度等要求，则采用的测温元件、测温方式以及对温度的控制方法也将不同。PID控制由于算法简单、可靠性高和鲁棒性好，被广泛运用于包括温度控制的各种控制过程中。由于控制理论本身面临着一些问题与困难，针对不同的系统需要不断地改进与提高。尽管大量新的控制算法不断涌现，但常规的PID及改进的PID控制算法仍然广泛应用于工业控制领域。

本文采用AT89S51单片机为核心，应用改进型PID算法，实现对电热锅炉的温度精确控制。简要介绍了设计方案，主要分析了控制部分所采用的改进PID算法的优势和实现方法。

控制算法从发展上来看分为经典PID控制和一系列的改进

PID控制。经典PID控制具有原理简单，使用方便的优点，

但针对一些具体的控制对象有可能出现饱和积分，超调量过大的问题，容易引起输出的大幅度变化；而在经典PID控制的基础上针对一些不同的控制对象和要求采取改进后的控制算法则更加优秀和适合。

图1

系统总体设计框图

PID控制算法中，积分的作用是为了消除静差，提高

控制精度。系统积分项的要求是：偏差大时积分作用应减弱甚至全无，而在偏差小时则应加强。对于温度过程对象变化比较缓慢且带有纯滞后环节，积分系数取大了会产生超调，甚至积分饱和，取小了又不能及时消除静差。因此，笔者在控制系统中提出根据测量值和设定值的偏差大小，来改变PID算法中积分项的累加速度，效果显著

k

［4］

2系统设计方案

电热锅炉温度控制系统由核心处理模块、温度采集模块、键盘显示模块和控制执行模块等组成。

采用比较流行的AT89S51作为电路的控制核心，使用

12位的高精度模数转换器AD574A进行数据转换，控制电

路部分采用PWM控制可控硅的通断以实现对锅炉温度的连续控制，此方案电路简单并且可以满足设计中的各项要求的精度。系统设计总体框图如图1所示

［1－3］

。

在此控制系统中，采用位置式的变速积分PID算法，其中原表达式中积分部分为K·i

。

3系统软件设计

3．1PID算法

系统算法控制采用工业上常用的PID数字控制。PID

收稿日期：2009－07－09

i＝0

ΣE

（i），引入一个与变

差E（k）有关的函数f［E（k）］，使积分变为：K·［f［E

i（k）］·E（k）＋

i＝0

ΣE

k－1

（i）］，则整个PID算式可以表达为：

本文设计了基于AT89s51的水温控制系统

机电工程技术年第38卷第12期

·［f［E（k）］·U（k）＝KcE（k）＋K·E（k）＋i

·［E（k）－E（k－1）］＋U0E（i）］＋Kd

i＝0

Σ

k－1

其中：Kc为PID控制比列系数；Ki＝Kc··Ts／Ti；Kd＝Kc

Td／Ts；Ti、Td、Ts分别为积分时间、微分时间和采样时间；U0为系统初始温度。

燮

M－E（k）＋M（k－1）

f［E（k）］＝0燮

E（k）＞M＋N

燮M＋N

N燮E（k）E（k）

＜N

1燮

燮

这样当温差变大时，积分部分的作用变小；温差很小时，积分部分的作用变大。而且这种变化跟E有关，能更好地适应系统的状态变化。对于温度控制系统，因为用户要求在升温阶段温度要快速上升，温度稳定时，上下波动范围要小，因此选取M＝1．5，N＝0．5。则在温度绝对范围小于0．5℃时全速积分：当温度绝对值范围在0．5℃～2℃以内时，积分部分逐步改变积分；当温度绝对值超出范围2℃以外时，则完全减小积分作用［5－6］。

电炉温控系统可以近似建立为具有滞后性质的一阶惯性环节数学模型。其传递函数形式为：

图2

PID程序流程图

G（s）＝

Ke－ts

式中：K、T分别为比例系数和时间系数；t为滞后时间系数。

3．2PID参数整定

首先选择一个足够短的采样周期使系统工作，本设计选取Ts＝40s；然后仅加入比例控制的环节，直到系统对输入的阶跃响应出现临界震荡，记下此时的比例系数震荡周期；根据公式计算出PID大概参数；再加入积分环节，减小超调量；最后加入微分环节，进行微调，直到输出满足要求为止。在本系统控制对象情况下，多次仿真调整参数后，得到Kc＝0．6，Ti＝160s，Td＝40s。

图3

仿真结果图

3．3PID程序设计

PID程序设计流程图如图2所示，首先给程序参数赋

予初值，再计算此时刻实际温度与要求温度的偏差，从而决定积分部分的大小，得出当前温度。以此循环最终使温度稳定在要求温度附近。

设计的思想，应该说，这种思想比控制系统本身更为重要。

参考文献：

［1］何立民．单片机中级教程［M］．北京：北京航空航天大学出

版社，2002．

［2］李朝青．单片机原理及接口技术［M］．北京：北京航空航天

大学出版社，1999．

［3］杨旭方．ProtelDXP实训教程［M］．北京：电子工业出版

社，2007．

［4］潘立登．过程控制技术［M］．北京：中国电力出版社，

3．4仿真结果

假设初始水温为20℃，需要加热到80℃，并使水温保持在80℃左右。具体仿真结果如图3所示（纵坐标为温度／℃，横坐标为时间／min）。由图可见采用变速积分PID控制后超调量小，上升时间较短，可以较好地满足温度的控制要求。

2007．

［5］黄道平．MATLAB与控制系统的数字仿真［M］．北京：化学

工业出版社，2004．

［6］李宜达．控制系统与仿真［M］．北京：清华大学出版社，

4结语

本文针对电热锅炉温度控制系统模型，提出了一种基于单片机AT89S51的设计方案。设计中运用变速积分PID算法，实现对温度的连续控制。设计的控制器工作稳定，控制精度高，改进的PID算法超调量小。本设计的目的不仅仅是温度控制本身，主要是提供了软件设计和控制算法

2004．

［7］王军伟，金燕．基于模糊理论的PID控制器设计方法及仿真

研究［J］．机电工程，2008（11）：38－40．

第一作者简介：徐志强，男，1983年生，

四川自贡人，硕士研究生。

研究领域：过程控制监控。

(编辑：吴智恒)

本文设计了基于AT89s51的水温控制系统

Abstracts

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Key words: leak detection machine; PLC; touching screen; man-machine contact surface

SONG Jia-wei1, XU Bo-qiang1, YE Lei2 (1.School of Electrical

Engineering, North China Electric Power University, Baoding 071003, China;2.Zheng zhou Electric Power Industry Bureau, Zhengzhou450000, China)

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Key words: induction motor; broken rotor bar fault; fault diagnosis; variable frequency power supply; power supply current

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